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NÉPHÉLOMÈTRE INTÉGRATEUR
Les néphélomètres intégrateurs sont des instruments d'analyse. Ils permettent de mesurer le coefficient de diffusion de la lumière des aérosols atmosphériques et de laboratoire sur de courtes ou longues périodes. Ils conviennent tout particulièrement aux mesures liées au climat, à la visibilité et à la qualité de l'air.
Ces instruments uniques sont sensibles à des coefficients de diffusion d'aérosols inférieurs à 2,0 x 10-7m-1. Cela représente deux fois la puissance de dix proposée par les appareils concurrents.
TSI propose des modèles dotés d'une ou trois longueurs d'onde. Le modèle trois couleurs permet la mesure des signaux totaux ou de rétrodiffusion. Les deux modèles sont entièrement gérés par la station de travail..
Caractéristiques et points forts
- Sensibilité à des coefficients de diffusion d'aérosols inférieurs à 2,0 x 10-7 m-1
- Temps d'intégration sélectionnable
Utilisation
- Climat, visibilité, et qualité de l'air
Contenu :
- Logiciel du néphélomètre
- Alimentation électrique
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Le modèle 3563 de TSI permet de mesurer le coefficient de diffusion de la lumière des aérosols atmosphériques et de laboratoire sur de courtes ou longues périodes. |
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NOTES D'APPLICATIONSERVICE PROCEDURESSTANDARD REPLACEMENT PARTSFOIRE AUX QUESTIONSshow/hide all answers
- Are nephelometer measurements independent of temperature and pressure? Does the instrument measure correctly at lower pressures?
The scattering values that TSI's nephelometer provides are the scattering values of the particles, no matter what the temperature or pressure might be. The scattering of particles is neither temperature nor pressure dependent! However, the total scattering measured by the instrument also includes contributions from air molecules (Rayleigh scattering) and the wall. Rayleigh scattering is temperature and pressure dependent, but it is well known. The instrument corrects for it automatically. The wall scatter is measured during a zero measurement. The corrected Rayleigh scatter, along with the measured wall scatter, are subtracted from the measured total to give the resulting particle scatter. Thus, TSI's nephelometer will measure correctly even at lower pressures (for example, on top of a mountain).
- Forcing seems to be one of the key words in the whole global climate change discussion. What does it actually mean?
Forcing means anthropogenic, that is, man-made, or externally imposed change to the planetary energy balance. So, the effects that aerosols generated by industry, combustion, and so forth have on the Earth's climate are part of the climate forcing. A good example of forcing is to picture the Kuwaiti oil fires during the Gulf War. The burning of the oil fields lasted for many days, generating a huge cloud of smoke. This situation had the potential for serious effects on the environment.
- How should I take a sample for my nephelometer?
A simple one-inch diameter tube extending out from the nephelometer inlet, or whatever distance is necessary to avoid contamination, is fine. If the tube is conductive, it minimizes the possibility of charged-induced losses. Sedimentation losses only occur for large particles (that is, larger than 5 µm), but these do not contribute significantly to particle scattering, especially since the forward scattering is not detected. The sample flow is provided by the nephelometer blower. Of course, the exhaust for the nephelometer should be filtered as for all other instruments.
- What is the BNC Input Voltage?
The BNC Input Voltage is intended as an analog input that can be used to monitor an event outside the nephelometer. You can, for example, monitor the sample temperature or relative humidity upstream of the instrument with an external sensor (needs to have 0 to 5 V analog output). You can then log this data with the rest of the nephelometer data for post analysis. In the past, the record of this input showed an oscillation when left unused. We now have reconfigured it to have a stable zero value when not in use.
- What is the difference between nephelometers with open and closed cavity design?
There are two schools of thought. One school says visibility is what they want to measure, at existing humidity, and the best way to do that is to use an open-cavity nephelometer, even though it eliminates water droplets that are bigger than a couple of 10 µm. Open-cavity nephelometers, therefore, allow fog and mist to affect the measurement. The other school says, because you cannot measure accurately at existing humidity, and because you are interested in apportioning fractions of the aerosol to a man-made source, you should try to control humidity. Closed-cavity design units, such as the TSI nephelometer, sample aerosol into a sensing zone, permitting the user to condition the sample so fog and mist do not affect the measurement. The preferred instrument depends on the purpose of the measurement. If aerosol pollution is of interest, fog and mist are interferences. The closed-chamber design allows the control of relative humidity (by heating), thus providing a separate measurement of the scattering coefficient and the increase in it due to relative humidity. This must occur because the necessary companion measurements (concentration, etc.) also must be measured at a point in space and at a known, low relative humidity. TSI nephelometers do this.
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